Many state of the art street lighting systems have the capability of dimming the light of the street lamps such that energy may be saved. The street lamps are, for example, dimmed to a lower light intensity between 11:00 pm and 5:00 am. The reduction of the emitted light intensity during these hours is possible because of the relatively low average traffic intensity during these hours. Street lighting systems are often subdivided into segments of streets lamps with a fixed length of, for example, 2 km. At intersections the segments have often different lengths. The desired light intensity emitted by the street lamps of each one of the segments may be controlled from a central location.
Published UK patent application G2444734A discloses an energy-efficient road lighting employing presence detection. The road lighting system has a dedicated activity detection system in which every lamp standard has a detection means for detecting vehicles in the immediate vicinity of the lamp standard. When a vehicle is detected, the direction of movement and the speed of movement are assessed. This information is communicated to neighboring lamp standards, for example, the lamp standards situated ahead. On the basis of the received information a controller of each one of the lamp standards decides whether the lamp has to emit light, or has to be switched off. Lamps situated ahead in the direction in which a vehicle is moving are switched on before the vehicle passes the lamp standard, and lamps passed by the vehicle are switched off.
A problem of the disclosed road lighting system is that each one of the lamp standards has to include a lot of hardware, like a detection means, a controller, and communication means. Thus, the system according to the UK patent is relatively expensive.